In the rotary atomizing electrostatic coating apparatus, when the paint adheres around the nozzle for spraying the paint, the paint scatters around with forced by the centrifugal force generated by high-speed rotation of the bell cup or by the air blown out from the shaping air ring, which is called a spit. When the paint adheres to the painted surface, the poor paint quality occurs. Thus, in the rotary atomizing electrostatic coating apparatus, in order to keep good paint quality, required is the technique of preventing the paint (blot) from adhering to the periphery of the nozzle.
In the conventional technique, needle electrodes are provided around the nozzle to form electrostatic fields around the electrodes so that the electrostatic repulsion is acted on the paint mist floating around the electrodes, keeping it away from the nozzle, thereby preventing the paint from adhering to the nozzle.
JP 2006-82064 A discloses the rotary atomizing electrostatic coating apparatus, which includes the needle electrodes radiating from the ring electrode, arranged at the periphery thereof to form uniform electrostatic field around the nozzle.
Referring FIGS. 7 to 10, the conventional blot preventing device 51 is explained below.
As shown in FIG. 7, the device 51 has an electrode part 54 including a ring electrode 52 and multiple (ten) needle electrodes 53 (53a, 53b, 53c, 53d, 53e, 53f, 53g, 53h, 53i, 53j) radiating from the ring electrode 52 each of which is spaced at the substantially equal distance, and the electrode part 54 is connected with a high voltage generator 56.
As shown in FIG. 8, in the actual using, the electrode part 54 is fixed to a coating gun 55. In detail, the electrode part 54 is arranged at the periphery of a shaping air ring 55b located backside of a bell cup 55a. 
As shown in FIG. 8, the high voltage generator 56 is built in the coating gun 55, electrically connected to a built-in air motor 55c and to a built-in wire 56a. 
The high voltage generator 56 is supplied with 24 V from the external source, in which the voltage is raised to about 90 kV. The high voltage generated in the generator 56 is applied to the air motor 55c. 
The air motor 55c is composed of conducting members and contacts the shaping air ring 55b which is also composed of conducting members. Thus, the air motor 55c and the shaping air ring 55b are electrically connected. The voltage applied to the air motor 55c is also applied to the bell cup 55a. 
The electrode part 54 is fixed to the ring 55b, so that they are electrically connected. The voltage applied to the ring 55b is applied to the electrode part 54.
As described above, the electrode part 54 is electrically connected to the high voltage generator 56 built in the gun 55, to which high voltage applied.
As shown in FIG. 9, the high voltage generated by the generator 56 is applied to the electrode part 54, whereby the needle electrodes 53 form the high-intensity electrostatic field (electric barrier) toward a grounded body 57. The paint mist discharged from the bell cup 55a of the gun 55 is controlled with the electrostatic repulsion, keeping the paint away from the gun 55, thereby preventing the paint from adhering to the gun 55 (especially to proximate portions to the bell cup 55a, shaping air ring 55b).
As shown in FIG. 9, when the electrode part 54 is apart from the grounded body 57 by the normal distance (in the normal state), the needle electrodes 53 foam the electrostatic field toward the grounded body 57 and the corona discharge occurs in which the slight current about a few μA flows from the electrodes 53 to the grounded body 57.
Unfortunately, as shown in FIG. 10, when the needle electrodes 53 come closer to the grounded body 57 beyond the proper range (namely, the distance between them becomes not more than the distance L1), the electric discharge amount increases and the discharge energy becomes higher, so that the discharge phase is shifted to the spark discharge from the corona discharge.
As depicted in FIG. 10, for example, when the distance between the needle electrode 53d and the grounded body 57 becomes the distance L2 (L2<L1, which is not more than the normal distance), the current concentrates on the electrode 53d, thereby increasing the electric energy in the electrode 53d and unfortunately generating the spark from the electrode 53d to the grounded body 57.
The conventional device 51 having the needle electrodes 53 is controlled to prevent the spark discharge. For instance, the discharge current is monitored and when the higher current than the predetermined value is detected, the power supply to the high voltage generator 56 is stopped or lowered.
In other case, when the electrode 53d come closer to the grounded body 57 beyond the proper range, the current concentrates on the electrode 53d, thereby dropping the voltages applied to the other electrodes (apart from the electrode 53d). Mentioned to the electrodes 53c and 53e, the distances from the grounded body 57 are the distance L3, which is in the proper range, however, the voltages dropped caused by the electrode 53d, whereby the electrostatic fields generated therefrom become less than the proper intensity. Moreover, the similar situation occurs in the other electrodes. As a result, the performance of the device 51 (blot preventing performance) is lowered.
The conventional device 51 can be applied to the case that the distance between the coating object and the gun 55 is easily kept in the proper range, for example when coating the exterior of the vehicle body. However, when coating the inside of the complex configuration such as the interior of the vehicle body, the gun 55 easily moves close to the coating object (flame or the like) beyond the proper range. In the close situation, the spark discharge or the voltage drop may occur, so that the measure is needed such as to stop the power supply to the electrodes 53. In such situation, the coating operation is interrupted, and the performance of the device 51 may fail to be kept properly.